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Old 12th October 2012, 11:51 AM   #11
ramallo is offline ramallo  Europe
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Stock with felt and rear chamber
Click the image to open in full size.
Dipole without felt
Click the image to open in full size.
1W
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Old 12th October 2012, 01:05 PM   #12
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That THD is the lowest I've ever seen for a loudspeaker driver. Its approx -60 dB, which is 0,1%.
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Old 12th October 2012, 01:45 PM   #13
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Quote:
Originally Posted by StigErik View Post
That THD is the lowest I've ever seen for a loudspeaker driver. Its approx -60 dB, which is 0,1%.
Yes, is the one of lowest THD I could measure (The other was a Quad ESL 63). This measure was made in my garden with a Earthworks M30 microphone and a Sound Devices USBPre soundcard
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Old 12th October 2012, 08:34 PM   #14
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Yes, is the one of lowest THD I could measure (The other was a Quad ESL 63). This measure was made in my garden with a Earthworks M30 microphone and a Sound Devices USBPre soundcard
So based on what you are showing, I really should remove the rear chamber! Just to make sure, both of those measurements were at the same SPL and under the same conditions? This is stock TPl versus dipole AND your magnet system or just the stock TPL run as a dipole?

I've played with the idea for a while, but never tried it. Hmmmmm, in my case I cannot leave it dipole, but I could make the chamber significantly larger and stuff well with Bonded Logic.

Greg
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Old 12th October 2012, 08:37 PM   #15
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Originally Posted by Lgrau View Post
Ok, then the issue is clear, no damping right behind the diaphram :-)
I wonder if the flimsy, shallow backcup is making problems. And also if the felt pad is too hard and reflective. A much deeper cup and better acoustical absorption placed father away from the diaphragm might be good.
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Old 12th October 2012, 08:46 PM   #16
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Quote:
Originally Posted by studiotech View Post
So based on what you are showing, I really should remove the rear chamber! Just to make sure, both of those measurements were at the same SPL and under the same conditions? This is stock TPl versus dipole AND your magnet system or just the stock TPL run as a dipole?

I've played with the idea for a while, but never tried it. Hmmmmm, in my case I cannot leave it dipole, but I could make the chamber significantly larger and stuff well with Bonded Logic.

Greg
By Removing the chamber and the felt mat.

Yes, at the same place and same SPL (ten minutes of difference).

The worst thing is the felt on the back of the TPL (is very dense), just removing this felt you can get better measures. Filling the camera with another material also improves a bit (foam).

Dipole mode is very good for THD, but the freq response is worse.
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Old 12th October 2012, 08:49 PM   #17
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Quote:
Originally Posted by studiotech View Post
I wonder if the flimsy, shallow backcup is making problems. And also if the felt pad is too hard and reflective. A much deeper cup and better acoustical absorption placed father away from the diaphragm might be good.
If the acoustic impedance of both sides isn't equal, you will have a 2 harmonic distortion increase
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Old 12th October 2012, 08:53 PM   #18
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When placing absorber a couple of inch back, it measures same as dipole.(EDIT in my setup) So using a larger enclosure with good damping should be the right approach.
But please keep in mind when removing the felt pad, you'll get more pronounced resonance at 1800Hz.

I expect to keep the back opened, but with quite heavy damping of the sound from the back of the driver. Made a test filling with rockwool this gave aprox 30dB attenuation.
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Old 12th October 2012, 08:59 PM   #19
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On my speakers I prefer so much a full dipole instead a dipole with heavy absorber on the back, IMMO sound much better

Click the image to open in full size.
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Old 12th October 2012, 09:59 PM   #20
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On the first TPL units, the membrane wasn't firmly secured, this causes some resonances at certain frequencies (Easily solved with a tape on the sides of the membrane).
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